feat(auth): add legal document pages and wire consent text links on sign-up screen

[coderabbitai]

Summary

The consent text in _ConsentRow on the sign-up page (lib/features/auth/presentation/pages/sign_up_page.dart) renders two underlined spans — "Политикой конфиденциальности" and "Согласие на обработку персональных данных" — that are styled as tappable links but have no TapGestureRecognizer or destination pages wired up. This is visually misleading to users.

Tasks

• Create LegalDocumentPage widget and register a route for it.
• Add TapGestureRecognizer instances to both underlined TextSpans in _ConsentRow.
• Dispose the recognizers in _SignUpPageState.dispose().
• Wire the recognizers to navigate to the respective pages.

References

• Flagged in PR: feat(auth): add sign-up flow and reusable auth form widgets #14
• Review comment: feat(auth): add sign-up flow and reusable auth form widgets #14 (comment)
• Requested by: @CowboyGH